The present invention relates to mass emory for computers having associative recall capability and, more particularly, to a multi-layered, thin-film, digital memory having associative recall comprising, a first memory matrix and a second memory matrix, each memory matrix comprising, (1) a first layer comprising a plurality of electrically separated row conductors; (2) a second layer comprising a plurality of electrically separated column conductors intersecting but electrically separated from the row conductors; and, (3) a plurality of resistance elements electrically connected between the row conductors and the column conductors at respective intersections of the row conductors and the column conductors, each resistance element comprising, in series, a first resistor of sufficiently high ohmage to conduct a sensible current therethrough with virtually no heat-generating power consumption when a low voltage as employed in thin-film applications is applied thereacross and a second resistor of sufficiently high ohmage to conduct no sensible current therethrough when a low voltage as employed in thin-film applications is applied thereacross, the second resistor having the quality of breaking down to create a short therethrough upon the application of a breakdown level voltage across the first and second resistors; a plurality of bi-stable sense amplifier means each having an input connected to a respective one of the column conductors of the second matrix for indicating at an output thereof when a current flow is detected at the input in the one of the column conductors of the second matrix connected thereto; a plurality of current summing amplifier means each having an output connected to a respective one of the row conductors of the second matrix for applying a voltage to the one of the row conductors of the second matrix connected thereto when the current into a second input thereof exceeds the current into a first input thereof, the row conductors of the first matrix being electrically connected to respective ones of the second inputs; a plurality of bi-stable read driver means each having an output connected to a respective one of the column conductors of the first matrix for outputting a voltage when an input thereof has a binary "1" prompt value applied thereto and for not outputting a voltage when the input thereof has a binary "0" prompt value applied thereto; and, ramped read driver means having an output connected to the first inputs of the current summing amplifier means for producing a downward ramp at the output thereof starting at a value higher than the maximum possible value at the second inputs and decreasing until one of the current summing amplifier means has its second input value higher than the output of the ramped read driver means and applies a voltage to the one of the row conductors of the second matrix connected thereto.
Computer memory has gone through much evolution in the short time that digital computers have been generally available. The original computers had only one memory--a rotating drum with a magnetizable surface rotating past a plurality of read and write heads. With the advent of so-called core memory for the "main" memory, there was a functional split between the main memory which was generally small (12-16K words), high priced, and bulky and mass memory that provided storage at a much lower price per word for large masses of data and programs that were only used occasionally. As depicted in FIG. 1, the early core memories 10 comprised a plurality of annular ferrite cores 12 strung on a matrix of row and column wires 14 and 16. The core memories offered random access to each word stored therein (i.e. equal access time) while the mass storage devices (such as the drum memories) had inherent access times caused by rotational delays of the drum with respect to the read heads. Later developed rotational mass storage devices such as disk drives reduced the size of the device; but, did nothing to overcome the rotational delays and, in fact, added additional delays in the form of arm movement radially in an out to position the heads on the disk.
More exotic developments in the memory art have provided main memory without the old ferrite cores and the ability to offer large memory matrices such as that indicated as 18 in FIG. 2 with no moving parts. The memory matrix 18 has row conductors 20 on one layer and column conductors 22 on an adjacent layer. The interconnections between the conductors 20, 22 are accomplished with transistors, or the like, which can be set to a "1" or "0" state (i.e. bi-stable or binary in nature) and then be read at a later time. Main memory is now routinely offered in mega-bytes with mass memory still limited to the use of rotational devices with their inherent limitations (imposed for a great part by a 3,00 rpm rotational maximum) or the use of main memory technology.
Space applications for computers have imposed additional constraints on memory technology. Many devices and technologies react unfavorably to the radiation encountered in space. At present, there is no memory available which offers large storage capacity in a small space employing thin film technology in a manner which has no moving parts and is radiation resistant.